At a thermal power plant or a nuclear power plant, feed water is converted into steam by a steam generator, and a turbine is driven by the steam in order to generate electric power. The steam used for driving the turbine is condensed by a condenser, then passes through a condensate treatment system for water treatment, and is fed back to the steam generator as feed water. The condensate treatment system used in a thermal power plant or in a nuclear power plant is required to be capable of processing a large amount of condensate, to be capable of stably ensuring water quality that is required for a power generating facility by removing soluble impurities (ionic impurities) and suspended impurities (clads) from the condensate, and to be capable of preventing ion components or foreign objects, which are included in seawater or lake water that is used as cooling water in a condenser, from entering the power generating system even when there is leakage of the seawater or the lake water.
Generally, a condensate treatment system includes a filtration apparatus that removes suspended impurities from condensate and a demineralization apparatus that removes ionic impurities. The demineralization apparatus is installed separately from and downstream of the filtration apparatus and holds cation exchange resin and anion exchange resin that are charged therein in a mixed-bed form. Only a demineralization apparatus, or a composite filtration and demineralization apparatus, in which filter elements are pre-coated with powdered ion exchanging resin, may be installed. Recently, a filtration apparatus and a demineralization apparatus are often installed separately in order to provide highly purified condensate water.
In a demineralization apparatus, ion exchangers that are charged in the apparatus are backwashed in order to stably obtain highly purified treated water. Alternatively, when the ion exchanging capacity of ion exchangers are saturated, the ion exchangers are removed from the demineralization apparatus and are re-charged in the demineralization apparatus after being regenerated by means of chemical reagents. The ion exchangers may be backwashed after they are removed from the demineralization apparatus. After the ion exchangers are backwashed or regenerated, the ion exchangers should be mixed by means of water or air when they are re-charged in the demineralization apparatus or while they are being backwashed, so that the cation exchange resin and the anion exchange resin, which are separated from each other due to a difference in specific gravity, are brought to a mixed state. The demineralization apparatus is then filled with filling water, such as condensate or pure water that is separately supplied. A circulation operation is then performed so that the ion exchangers adsorb or fix a small amount of regenerants that remains in the demineralization apparatus and fine particles that are generated when the ion exchangers are backwashed or transferred. The circulation operation is performed by circulating the filling water through the demineralization apparatus after the apparatus is filled with the filling water, then by using a re-circulating pump to pressurize the circulating water that is discharged from the demineralization apparatus, and then by feeding back the circulating water to a point downstream of the filtration apparatus or upstream of the demineralization apparatus. When the system requires degassed water, a degassing operation may be performed prior to the circulation step by replacing the filling water in the demineralization apparatus with condensate (degassed by the condenser). This circulating operation prevents the remaining regenrerants or the fine particles from leaking into the condensate, allowing the demineralization apparatus to generate highly purified treated water immediately after it receives water that is to be treated.
When the filtration apparatus and the demineralization apparatus are installed separately, each apparatus individually requires components, such as a tank, a pump, valves, lines and a control board. It is also necessary to individually supply makeup water, compressed air used as service air and instrumentation air and so on, which are required for operating the apparatus. This causes a problem that a large amount of space is needed in order to install the filtration apparatus and the demineralization apparatus, and accordingly this causes a problem that the building cost and the cost of the apparatus increases. To deal with the problems, a report was made regarding a filtration and demineralization apparatus that includes a hollow fiber membrane, wherein the hollow portion of the membrane is filled with ion exchanging resin (e.g., Patent Document 1). Another filtration and demineralization apparatus has a column that houses a hollow fiber membrane module, as well as ion exchangers (e.g., Patent Document 2). There is a report on a composite filtration and demineralization apparatus in which a filtration apparatus and a demineralization apparatus are integrated (e.g., Patent Document 3) in one vessel. The inside of the vessel is divided into an upper chamber that houses hollow fiber membrane modules and a lower chamber that is filled with ion exchangers.
Patent Document 1: JP 06-170363A
Patent Document 2: JP 62-83003A
Patent Document 3: JP 08-117746A